Apparatus for the calibration of optical measuring instruments

ABSTRACT

An apparatus ( 1 ) for the calibration of optical measuring instruments ( 10 ) with a carrier ( 2 ). According to the invention the calibration body ( 4 ) has a glass body ( 4 ) which has at least one scattering element ( 42 ), wherein this scattering element ( 42 ) is completely surrounded by the glass body ( 4 ), wherein a degree of transmission of the scattering element ( 42 ) and of the glass body differ from each other.

The present invention relates to an apparatus for the calibration and/ortesting of measuring instruments. Various optical measuring instrumentsare known from the prior art. The invention relates in particular to ameasuring instrument for the investigation of characteristics ofsurfaces. In addition, instruments of this type have long been knownfrom the prior art. In this case it is known, in particular, for asuitable measuring instrument to be guided over a surface to beinvestigated and for this surface to be illuminated in this case and forinformation to be gathered from the radiation reflected or scatteredrespectively.

In this case it is necessary, however, for these measuring instrumentsto be newly calibrated from time to time. For this purpose calibrationappliances or standards respectively are known from the prior art. Thesecalibration appliances usually have in this case a carrier along whichthe measuring instrument can be guided, in which case it illuminates acalibration body. Information, can be gathered from the radiation thrownback or reflected respectively or scattered accordingly by thecalibration body, and calibration or adjustments respectively can becarried out again on the basis of this information. In this case thesecalibration appliances are frequently subjected to relatively roughhandling. In part these calibration appliances are soiled and arecleaned with abrasive cleaning agents. In addition, a change in therespective calibration bodies frequently occurs as a result of ageingprocesses. In this way, after a certain amount of time they are nolonger capable of being used for the purpose intended for them.

The object of the present invention is therefore to improve theresistance and preferably also the durability of calibration appliancesof this type. This is achieved according to the invention by thesubjects of the independent claims. Advantageous embodiments and furtherdevelopments form the subject matter of the sub-claims.

An apparatus according to the invention for the calibration of opticalmeasuring instruments has a carrier. In addition, the apparatus has acalibration body arranged on the carrier.

According to the invention this calibration body has a glass body whichin turn has at least one scattering element, this scattering elementbeing completely surrounded by the glass body and a degree oftransmission of the scattering element and of another region of theglass body differing from each other with respect to light striking thecalibration body). It is advantageous for this calibration body to serveas a calibration standard and/or test standard.

It is therefore proposed according to the invention that a calibrationbody should be provided which has scattering elements differingoptically (with respect to the glass body), but these scatteringelements—other than in the prior art—are arranged not on a surface ofthe calibration body but in an inner space. In this way, the aforesaidscattering elements are not susceptible themselves to damage and soilingand, in addition, to ageing processes and also to cleaning processes. Inthe case of a further advantageous embodiment the contacting element orthe calibration body respectively is arranged on the carrier in a fixedmanner. In this case it is possible for the calibration body to bescrewed or glued to the carrier in a fixed manner or to be fastenedthereto by other fastening means. In this way, it is possible to ensurethat the calibration body cannot shift with respect to the carrier, sothat the reliability of the appliance is increased as a whole.

In the case of a further advantageous embodiment the scattering elementis a scattering element produced by a laser treatment of the glass body.This means that these scattering elements are produced with the aid ofmethods known from the prior art in the interior of the glass body, forexample by a local melting of the glass material being carried out inthe interior. This can be carried out for example by a so-called 3Dlaser engraving. In this way, it is possible for the scattering element,as mentioned above, to be situated in the interior of the class body andnot on the outer surface thereof.

It is also possible, with the aid of laser treatments or laserirradiation of this type respectively, for the depth—by which thescattering element is produced—inside the glass body to be fixed.

In the case of a further preferred embodiment the carrier has a guidedevice which guides the measuring instrument to be calibrated in such away that the measuring instrument is movable with respect to the carrieralong a pre-defined line.

It is advantageous for the line along which the measuring instrument canbe displaced with respect to the carrier to be a straight line. It wouldalso be possible, however, for the calibration body to be incorporatedin a measuring instrument in a stationary manner. In this way, themeasuring instrument can have for example an irradiation or illuminationdevice which in normal operation illuminates a material to beinvestigated and which in a calibration or testing operation illuminatesthe calibration body. It is preferable in an embodiment of this type forthe measuring instrument to have a sensor device which is arrangedbehind the calibration body in the illumination direction. In the caseof an arrangement of this type, the carrier is preferably used toposition the calibration body in an unambiguous and, in particular,fixed position.

In this case it is preferable for the calibration body or standardrespectively to be held in a ring (i.e. this ring constitutes thecarrier in this case) and to be held on a sample well. The ring ensuresan exact positioning in order to obtain reproducible measurement values.

In the case of a further advantageous embodiment the guide device has afirst guide rail in which at least one wheel of the measuring instrumentcan roll. Measuring instruments of this type frequently have wheels bymeans of which they can roll with respect to a surface to beinvestigated, for example the surface of the bodywork of a motorvehicle. The guide device is designed in such a way that this wheel canalso roll with respect to the guide device.

It is advantageous for the apparatus also to have a second guide railwhich in a particularly preferred manner is parallel to the first guiderail and in which at least one wheel of the measuring instrument canlikewise roll. It is advantageous for the measuring instrument to havefour wheels, two of these wheels running in one guide rail in thecalibration operation and the other two wheels running in the otherguide rail.

It is preferable for the guide rail or the guide device respectively toallow a movement of the measuring instrument in only one direction, butnot in a direction at a right angle to this. For this purpose a width ofthe guide rail can be adapted to a width of the wheels of the measuringinstrument, for example it can be selected to be only slightly larger.In addition, protection mechanisms, which prevent damage to outersurfaces of the wheel of the measuring instrument, can be present on orin the guide rail. On account of this special design of the guide railthe measuring instrument is prevented from being capable of being movedtransversely to its direction of movement with respect to the carrier.

It is advantageous for the guide rail, or a surface on which the wheelof the measuring instrument rolls respectively, to be situated atsubstantially the same height as a surface of the calibration body. Inthis way, an actual measurement situation on a surface, for example of amotor vehicle, can be adjusted in a reliable manner.

It is preferable for the scattering element to scatter light of theapparatus irradiated onto it. It would also be possible, however, forthe scattering element to be an element which is reflecting rather thanscattering.

In the case of a further advantageous embodiment a transmission or atransmission capability of the scattering element is less than atransmission capability of the areas surrounding the scattering element.It is advantageous for a plurality of scattering elements of this typeto be formed in the glass body and these are preferably arranged at adistance from one another along the direction of movement of themeasuring instrument. In this way, an undisturbed glass body can beformed for example between the individual scattering elements, and, inthis way, it has a very high degree of transmission. It would also bepossible, however, for a scattering element with a specifiedtransmission to merge into a further scattering element with atransmission different therefrom.

It would also be possible for a plurality of scattering elements to bearranged one behind the other in such a way that when these scatteringelements are read out the measuring instrument emits a specified value.In this way, a specified sequence of the scattering elements in theglass body can also be used for the calibration of the measuringinstrument. In other words, it is possible for the scattering elementsto be arranged inside the calibration body in the manner of a barcode.This barcode can be characteristic of one or more spatial frequencies(number of the periods per unit of length) of the appliance in thiscase.

If a measurement value (for example a degree of brightness) is recordedwith respect to the spatial frequency, and in particular within thescope of a one-dimensional movement, the level of a measurement valuecan be influenced with the aid of the production of defined patterns(for example a barcode).

Variations in the brightness are produced for example by the arrangementof specified patterns. In this way for example, the calibration body canhave a defined sequence of patterns. If the brightness of a pattern ofthis type is scanned with the aid of a measuring instrument, thevariations in the brightness measured can be converted by mathematicalfilters into measures for the variation in the brightness of a specifiedspatial frequency or of a spatial frequency range, which are preferablyemitted as measurement values. The patterns or scattering elementsrespectively can preferably be arranged in such a way that a testingstandard is achieved with measurement values in the operating range ofthe measuring instrument. In this case a brightness scan for example canfirst be recorded and the values measured (in a spatially dependentmanner) in each case can be processed by means of mathematic filters inorder to obtain the measurement values dependent upon the spatialfrequency in this way.

It is preferable for a plurality of scattering elements with differentwidths or different lengths of extension respectively (in a direction ofmovement of the measuring instrument) to be provided.

In the case of a further advantageous embodiment the calibration body isarranged on the carrier in such a way that a surface of the calibrationbody faces along the pre-set line towards the measuring instrument to becalibrated. This means that the calibration body preferably extends sofar that it can be illuminated by an illumination device of themeasuring instrument along the entire path thereof with respect to thecarrier device.

The invention has also been described in this case to the effect thatthe measuring instrument is moved with respect to the carrier. It wouldalso be possible, however, for the measuring instrument itself to be atrest as compared with the carrier and, instead, for the calibration bodyto be moved relative to the carrier and/or the measuring instrument. Inthis way for example, the calibration body itself could be arrangedinside a rail and be moved with respect to this rail. An arrangement ofthis type would also be advisable for measuring instruments which haveno wheels for example.

In addition, a holding device movable with respect to the carrier in apre-set direction of movement could also be arranged on the carrier. Themeasuring instrument to be calibrated could be arranged in turn on thisholding device. In this way, fastening devices could be present whichfix the measuring instrument with respect to the holding device.

In the case of a further advantageous embodiment the surface of thecalibration body facing the measuring instrument is a smooth surface. Itis preferable for the surface also to be a flat surface. In particular,by means of the provision of a glass body, and in this case againpreferably by means of the provision of a smooth glass body, thesusceptibility thereof to soiling and cleaners for example can bereduced. In addition, when soiling occurs, it is possible to clean thecleaning body very easily.

In the case of a further advantageous embodiment the calibration body isarranged on the carrier in such a way that only one surface of thecalibration body is capable of being contacted. In this way, thecalibration body is protected very well from outside influences. Inparticular, the calibration body is also well protected from soiling inthis way. If soiling does nevertheless occur, it can be removed veryeasily. If, as mentioned above, the calibration body is arrangeddirectly on a part of the carrier, for example glued, the formation ofgaps into which dirt can penetrate can also be prevented in this way.

In the case of a further advantageous embodiment the carrier is formedin at least two parts and the calibration body is arranged at leastpartially between these two parts of the carrier. In this case it ispossible for a part of the carrier to have a recess through which thecalibration body is visible. It is advantageous in this case for thecalibration body to be arranged between the two guide rails mentionedabove for the guidance of wheels of the measuring instrument.

The present invention further relates to a calibration body or test bodyrespectively for the calibration and/or testing of optical measuringinstruments. In this case this calibration body has a glass body whichhas at least one scattering element, this scattering element beingcompletely surrounded by the glass body and a degree of transmission ofthe scattering element and the glass body differing from each other andthe calibration body being designed, in addition, in one piece, thescattering element being a scattering element produced by lasertreatment of the glass body.

With respect to the calibration body a procedure is therefore alsoselected according to which the scattering element is incorporated intothis calibration body, it being advantageous for this calibration bodyto be a one-piece glass body. In particular, the treatment by laserallows such an (internal) design of a scattering element.

The design of the scattering element can be influenced by this lasertreatment. In particular, the scattering effect and/or the degree oftransmission of the scattering elements can be influenced. It ispreferable for the calibration body to have scattering elements withdifferent degrees of transmission and/or scattering.

It is advantageous for the calibration body to be produced from auniform material. It is preferable for the scattering elements toconsist of the same material as other areas of the calibration body. Itis preferable for the calibration body to consist of borofloat glass.

In the case of a further advantageous embodiment at least one surface ofthe glass body is a plane and/or a smooth surface. In this way, asmentioned above, the cleaning capacity of this glass body can beimproved.

In the case of a further advantageous embodiment a thickness of thisglass body is between 1 mm and 30 mm, preferably between 2 mm and 20 mmand in a particularly preferred manner between 3 mm and 7 mm.

These thicknesses of the glass body are suitable in this case in aparticular manner for also allowing a high degree of transmission forlight on those surfaces in which no scattering elements are present.

In the case of a further advantageous embodiment the glass body has acuboidal design. Round designs such as for example in the form of(circular) discs, however, would also be possible.

It is advantageous for the scattering element to be at a distance of atleast 1 mm from two opposed surfaces. It is advantageous in this casefor one of these surfaces to be a surface which faces the measuringinstrument in the calibration operation. In this case it is furtherpossible for residual glass bodies to be completely transparent. Itwould also be possible, however, for the rest of the glass body also notto be transparent or only transparent in part respectively and to have apre-set scattering proportion. In this case it is also possible for therest of the glass body also to have been treated by laser action.

In the case of a further advantageous embodiment the glass body has aplurality of scattering elements. It is preferable for these scatteringelements to be arranged at a distance from one another at least in part.In addition, it is also possible for these scattering elements to havedifferent lengths with respect to the calibration body along thedirection of movement of the measuring instrument.

In the case of a further embodiment a plurality of scattering elementsare arranged one behind the other with respect to the calibration bodyin a direction of movement of the measuring instrument.

In this case it is possible for the scattering element to be designed inthe form of flat faces, for example of rectangles. It would also bepossible, however, for the scattering elements to be designed in theform of figures, and in particular in the form of signs such as letters.In addition, it is also possible for the calibration body to be producedfrom a coloured glass.

In the case of a further advantageous embodiment the scattering elementor at least one scattering element respectively has a substantiallyhomogeneous structure. This is understood to mean for example that adegree of transmission of this scattering element does not change alonga direction of movement of the measuring instrument.

In the case of a further advantageous embodiment at least one surface ofthe calibration body is provided with a coating, and in particular butnot exclusively with a lacquer coating. This can be for example a whitecoloured surface. It would also be possible for the coating to be madereflecting. In addition, this coating could also be absorbing or kept ina dark colour respectively. In general, it is preferable for at leastone surface of the calibration body to be provided with a coating. It isadvantageous for this to be a coating which changes a transmissioncharacteristic of the calibration body.

It is preferable for the coating to be a homogeneous coating. It wouldalso be possible, however, for the coating to be deliberatelynon-homogeneous, for example a degree of reflection of this coatingchanges in the direction of movement of the measuring instrument withrespect to the calibration body.

It is advantageous for the aforesaid coating to be provided on thatsurface which is opposite the surface of the calibration body whichfaces the measuring instrument. In this way, it is advantageous for thiscoating or layer of lacquer respectively to be provided on a surface ofthe calibration body which faces away from the measuring instrument. Itis advantageous for the calibration body also to have a constantthickness along the direction of movement of the measuring instrumentwith respect to the calibration body.

In addition, the coating could also be provided as a scattering coating.

The present invention further relates to the use of a laser-treatedglass body for the calibration and/or testing of optical measuringinstruments, and in particular for the calibration of those opticalmeasuring instruments which are used for the detection of properties ofsurfaces. It is advantageous for this to be a glass body of the typedescribed above, in the internal structure of which scattering elementshave been formed by means of a laser treatment. It is advantageous inthis case for the laser-treated glass body to be used in such a way thatthe instrument to be calibrated is moved and/or adjusted or arrangedrespectively relative to the measuring body for the calibration andilluminates the latter at least for a time. In addition, the measurementvalues output by the measuring instrument can be monitored and, inparticular, compared with reference values.

Further advantages and embodiments are evident from the accompanyingdrawings. In the drawings

FIG. 1 is an illustration of an apparatus according to the invention forthe calibration of measuring instruments;

FIG. 2 is a plan view of a calibration body;

FIG. 3 is a further plan view and a side view of a calibration bodyaccording to the invention;

FIG. 4 shows a further embodiment of the present invention, and

FIG. 5 is an enlarged illustration of the carrier.

FIG. 1 shows an apparatus 1 according to the invention for thecalibration of optical measuring instruments, a measuring instrument 10being involved in this case which is used for investigating propertiesof surfaces, in particular of motor vehicle surfaces.

This measuring instrument has in this case a housing 52 in the interiorof which at least one radiation device and at least one radiationdetector device are preferably arranged. In addition, the measuringinstrument 10 has a display 56 with the aid of which information can beoutput to the user. On its underside or the side facing the carrier 2respectively the measuring instrument 10 has an opening (not visible)through which radiation, and in particular light, can emerge from themeasuring instrument 10. Expressed in more precise terms, this light canstrike the calibration body.

The reference number 54 refers to wheels which are arranged on thehousing or on the measuring instrument respectively and by which themeasuring instrument can be moved with respect to a surface to beinvestigated.

The reference number 2 refers to a carrier of the calibration apparatus.This carrier 2 serves in this case for guiding the measuring instrument10. For this purpose the carrier 2 has two guide rails or guide devicesor guide rails 6 respectively. These guide rails can have in this caserunning faces for the measuring instrument. These guide rails extend inthis case in the direction of movement B of the measuring instrument andhave the effect that, although the measuring instrument can be moved inthis direction, it cannot be moved in a direction at a right angle tothis. It would also be possible for the carrier to have arranged on itonly lateral guides which prevent a lateral transverse movement of themeasuring instrument with respect to the carrier 2.

The reference number 4 designates a calibration body which is arrangedon the carrier. In particular, this calibration body 4 is glued to anupper part 2 a of the carrier 2.

The reference number 8 designates a recess or a hole respectivelythrough which the calibration body 4 or the surface thereof respectivelyis accessible and, in this way, can also be irradiated by anillumination device of the measuring instrument 10. The reference number14 designates a lateral edge which bounds the carrier but which alsoprevents a movement of the measuring instrument 10 in a direction at aright angle to the direction of movement B.

The reference number 16 designates a protection mechanism which isattached to this lateral edge and which for example prevents surfaces ofthe individual wheels 54 from being scraped. This protection mechanismcan be for example a protective film which is attached, for exampleglued, to the carrier. The reference number 18 designates a fasteningelement by which the two parts of the carrier 2 are fixed to each other.

FIG. 2 is a plan view of a calibration body 4. This calibration body hasin this case a plurality of scattering elements 42 as well as atransparent main body 44 which in this case adjoins the scatteringelements in each case. In the case of the embodiment shown in FIG. 2 thetransparency of the portion 44 of the main body is very high and thetransparency of the scattering elements is lower as compared with thelatter. In this case the scattering elements are preferably arranged insuch a way that different spatial frequencies of the measuringinstrument can be taken into consideration.

FIG. 3 shows a comparison of a plan view with a side view of acalibration body 4. The surface 4 a of the calibration body, which facesthe measuring instrument during operation, is again evident in thiscase. It will be noted that the individual scattering elements 42 areembedded in the calibration body or the glass body thereof respectivelyand, in this way, are not accessible from any side (for a user). In thisway, it is possible to ensure that these scattering elements are notsusceptible to mechanical influences on the one hand, but are also notsubject to any ageing process on the other hand.

FIG. 4 shows a further embodiment or application respectively of thepresent invention. In the case of this embodiment the measuringinstrument 10 to be tested is an instrument in which an illuminationdevice illuminates the inner wall of a (spherical) body by way of asample to be investigated (or through the latter respectively). For thepurpose of testing and/or calibration, instead of the sample to beinvestigated, the calibration body is pressed into the beam path betweenthe illumination device and at least one sensor device. In the case ofthis embodiment no relative movement therefore takes place between themeasuring instrument and the calibration body 4. The reference number 62designates a spherical body into which the light is irradiated throughthe sample (or the calibration body respectively).

The reference number 2 refers in turn to the carrier, on which thecalibration body 4 is arranged.

FIG. 5 is an enlarged illustration of the carrier 2. The latter has anannular holding body for holding the calibration body. The referencenumber 24 designates a projection by which it is possible to ensure thatthe carrier is fastened on the measuring instrument in a preciselydefined rotational setting. The reference number 22 designates acarrying body such as for example a carrying ring for carrying orholding respectively the calibration body 4.

All the features disclosed in the application documents are claimed asbeing essential to the invention, insofar as they are novel eitherindividually or in combination as compared with the prior art.

LIST OF REFERENCES

-   1 apparatus according to the invention-   2 carrier-   2 a upper part-   4 calibration body-   4 a surface-   6 guide devices-   8 recess-   10 measuring instrument-   14 lateral edge-   16 protection mechanism-   18 fastening element-   22 carrying body-   24 projection-   42 scattering elements-   44 portion of the main body-   52 housing-   54 wheels-   56 display-   62 spherical body-   B direction of movement

1. An apparatus (1) for the calibration and/or testing of opticalmeasuring instruments (10) with a carrier (2), and with a calibrationbody (4) arranged on the carrier (2), characterized in that thecalibration body (4) has a glass body (44) which has at least onescattering element (42), wherein this scattering element (42) iscompletely surrounded by the glass body (44), wherein a degree oftransmission or degree of scattering respectively of the scatteringelement (42) and of the glass body (44) differ from each other.
 2. Anapparatus (1) according to claim 1, wherein the scattering element (42)is a scattering element (42) produced by a laser treatment of the glassbody (44).
 3. An apparatus (1) according to claim 1, wherein the has aguide device (6) which guides the measuring instrument to be calibratedin such a way that the measuring instrument is movable with respect tothe carrier (2) along a pre-defined line.
 4. An apparatus (1) accordingto claim 1, wherein the calibration body (4) is arranged on the carrier(2) in such a way that a surface (4 a) of the calibration body (4) facesalong the pre-set line towards the measuring instrument (10) to becalibrated.
 5. An apparatus (1) according to claim 3, wherein thesurface (4 a) is a smooth surface.
 6. An apparatus (1) according toclaim 3, wherein the calibration body is arranged on the carrier in sucha way that in a manner dependent upon a position of the measuringinstrument (10) with respect to the carrier an illumination device ofthe measuring instrument illuminates the scattering element (42) or afurther region of the glass body, the transmission of which differs fromthat of the scattering element (42).
 7. An apparatus (1) according toclaim 3, wherein the calibration body (4) is arranged on the carrier insuch a way that only one surface (4 a) of the calibration body (4) iscapable of being contacted.
 8. A calibration body (4) for thecalibration and/or testing of optical measuring instruments, whereinthis calibration body (4) has a glass body (44) which has at least onescattering element (42), wherein this scattering element (42) iscompletely surrounded by the glass body (44), wherein a degree oftransmission of the scattering element (42) and the glass body (44)differ from each other and wherein the calibration body (4) is designedin one piece, and the scattering element (42) is a scattering element(42) produced by laser treatment of the glass body.
 9. A calibrationbody (4) according to claim 8, wherein at least one surface (4 a) of theglass body (44) is a plane and/or a smooth surface.
 10. A calibrationbody (4) according to claim 8, wherein the scattering element (42) has asubstantially homogeneous structure.
 11. A calibration body (4)according to claim 8, wherein at least one surface of the calibrationbody (4) is provided with a coating.
 12. Use of a laser-treated glassbody for the calibration and/or testing of optical measuringinstruments.